Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $38.83   13.757%   $44.1718   $44.17   $44.15   $44.20  
  Purchase #2 $233.79   5.463%   $246.5619   $246.56   $246.55   $246.60  
  Purchase #3 $121.36   8.705%   $131.9244   $131.92   $131.90   $131.90  
  Purchase #4 $206.86   13.111%   $233.9814   $233.98   $234.00   $234.00  
  Purchase #5 $200.55   4.211%   $208.9952   $209.00   $209.00   $209.00  
  Purchase #6 $119.60   10.671%   $132.3625   $132.36   $132.35   $132.40  
  Purchase #7 $124.75   13.562%   $141.6686   $141.67   $141.65   $141.70  
  7 purchase totals = $1,045.74       $1,139.6658   $1,139.66   $1,139.60   $1,139.80